Sand washing temporary plugging agent and preparation method thereof

Abstract

The invention provides a sand washing temporary plugging agent and a preparation method thereof, and belongs to the technical field of oilfield chemistry. The sand washing temporary plugging agent comprises bridging particles and a filling material, and the bridging particles are of a core-shell structure and comprise from inside to outside an inner core formed by a compression-resistant material; the inner shell is formed by thermosetting resin and a curing agent, and materials in the inner shell can be continuously cured and bonded into a whole under the temperature condition of a target stratum; the melting point of the paraffin is lower than the temperature of the target stratum; the shell is formed by calcium carbonate and a disintegrating agent; and the waterproof protective shell is formed by calcium carbonate. According to the bridging particle, the shell and the waterproof protective shell are both brittle calcium carbonate shells, are combined into a whole and are easy to break when bearing external pressure, the shell is added with the disintegrating agent, and can rapidly absorb water to swell after meeting water, so that the shell and the waterproof protective shell are broken into fragments together, a seepage channel of a temperature-sensitive bonding material among particles is increased, and the temperature-sensitive bonding material is not prone to cracking. And the loading capacity of the solidified integrated structure is enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield chemistry, and in particular relates to a temporary plugging agent, specifically a sand flushing temporary plugging agent and a preparation method thereof. Background Art

[0002] Sand flushing temporary plugging agent is a key chemical agent used to temporarily plug formation pores or cracks in oil and gas field exploitation and well repair operations to prevent excessive leakage of sand flushing fluid and ensure the smooth progress of sand flushing operations. It usually adopts granular temporary plugging agent, which mainly includes granular material and filling material. When used, the granular material overlaps and supports each other in the cracks to form a porous skeleton structure, and the filling material fills the pores of the porous skeleton structure to form a plugging layer. Later, the temporary plugging agent material is degraded by itself or dissolved by acid injection to achieve unblocking.

[0003] To increase the pressure-bearing capacity of the plugging layer, some temporary plugging agents incorporate water-swelling materials, causing the plugging layer to further expand and compress, increasing its density. Other temporary plugging agents incorporate temperature-sensitive adhesives, leveraging their curing and bonding under formation conditions to form a single structure, thereby increasing migration resistance within the fracture. The latter, in particular, often exhibit higher pressure-bearing capacity. However, the viscosity of temperature-sensitive adhesives increases with temperature, making them prone to clumping during migration, increasing their size and preventing them from entering the target fracture. In this regard, a Chinese patent with publication number CN118291106A proposes a temporary plugging agent with a core-shell structure, which uses a pressure-resistant material as a core, a temperature-sensitive adhesive material as an inner shell, and a calcium carbonate coating as an outer shell. The "brittle + inert" calcium carbonate shell protects the temperature-sensitive adhesive material to prevent it from sticking together during migration. After the temporary plugging agent reaches the target crack and bridges it, it uses the pressure difference between the front and back of the plugging layer to crush the shell, so that the temperature-sensitive adhesive materials contact each other and consolidate into one. However, the calcium carbonate shell is almost solid material. When subjected to extrusion, the deformation of the calcium carbonate shell is small, and the problem of "breaking but not shattering" often occurs. That is, the extrusion effect only forms a limited number of cracks on the shell, but the shell is still adhered to / wrapped around the outer wall of the temperature-sensitive material. The temperature-sensitive adhesive material can only penetrate through the cracks to achieve solidification and bonding between the particles. There are few connection points between the particles, resulting in insufficient pressure bearing strength of the entire integrated structure. Summary of the Invention

[0004] To solve the above problems, the purpose of the present invention is to provide a sand flushing temporary plugging agent and a preparation method thereof. The outer shell and the waterproof protective shell of the present invention are both brittle calcium carbonate shells, which are combined into one body and are easily broken when subjected to external pressure. A disintegrant is added to the outer shell, which can quickly absorb water and expand when exposed to water, driving the outer shell and the waterproof protective shell to break into fragments together, increasing the seepage channel of the temperature-sensitive adhesive material between the particles, and enhancing the pressure-bearing capacity of the integrated structure after solidification.

[0005] To achieve the above objectives, the technical solutions of the present invention are as follows: A sand flushing temporary plugging agent, comprising bridging particles and a filling material, wherein the bridging particles are a core-shell structure and comprise, from the inside to the outside: a core formed of a compression-resistant material; The inner shell is formed of thermosetting resin and curing agent. The material in the inner shell can continue to solidify and bond into one piece under the temperature conditions of the target formation; An intermediate layer formed of paraffin wax, the melting point of which is lower than the temperature of the target formation; a shell formed of calcium carbonate and a disintegrant; Waterproof protective shell formed from calcium carbonate.

[0006] In the present invention, the ratio and size of the bridging particles and the filler material can be designed according to the design requirements of conventional plugging materials based on data such as crack size. The core of the present invention can be made of either an inorganic material or an organic polymer material. If an inorganic material is selected, it can be modified with a silane coupling agent to more evenly coat the thermosetting resin on the surface of the inorganic material. The inorganic polymer material can be a high-temperature resistant organic polymer material such as polyphenylene sulfide, polyimide, organopolysilazane, or polytetrafluoroethylene.

[0007] In the present invention, the material in the inner shell can continue to solidify and bond together under the temperature conditions of the target formation. This requires ensuring that there is still unreacted curing agent after the bridging particles reach the target formation, that is, secondary curing can be achieved, which can be achieved in a variety of ways. As a specific embodiment of the present invention, the curing agent is a composite curing agent, which includes two curing agents with different initiation temperatures, namely a low-temperature curing agent and a high-temperature latent curing agent, wherein the initiation temperature of the low-temperature curing agent is lower than the initiation temperature of the high-temperature latent curing agent, and the initiation temperature of the high-temperature latent curing agent is lower than the temperature of the target formation. The temperature difference between the initiation temperature of the high-temperature latent curing agent and the temperature of the target formation can be selected as needed to ensure that the high-temperature latent curing agent can continue to solidify after reaching the target formation.

[0008] As a specific embodiment of the present invention, the disintegrant is sodium carboxymethyl starch granules, low-substituted hydroxypropyl cellulose granules or cross-linked polyvinyl pyrrolidone granules. The present invention mainly utilizes the rapid swelling property of the disintegrant to break the outer shell and the waterproof protective shell.

[0009] As a specific embodiment of the present invention, the mass content of the disintegrant in the shell is 1% to 6%.

[0010] As a specific embodiment of the present invention, the thermosetting resin is an epoxy resin, a phenolic resin, a bismaleimide resin or a cyanate resin.

[0011] A method for preparing a sand flushing temporary plugging agent, for preparing the above-mentioned sand flushing temporary plugging agent, comprises the following steps: S1, using silane-modified ceramsite as the core and epoxy resin as the thermosetting resin, dispersing the silane-modified ceramsite, epoxy resin and curing agent in a solvent under stirring conditions, heating to preliminarily cure the epoxy resin, then removing the solvent, dispersing and drying the resulting material to obtain ceramsite particles covered with an epoxy resin coating (inner shell); S2. Adding the ceramsite particles coated with the epoxy resin coating into the molten paraffin liquid under stirring conditions, then taking out and cooling the ceramsite particles to obtain ceramsite particles coated with the paraffin coating (middle layer); S3, adding the paraffin-coated ceramsite particles to a heated polyvinyl alcohol aqueous solution under stirring, then letting it stand, taking it out to solidify and air-drying it to obtain ceramsite particles covered with a polyvinyl alcohol coating; S4, adding a disintegrant to triethylamine and ultrasonically dispersing the mixture to obtain triethylamine containing a disintegrant; dissolving anhydrous calcium chloride in an anhydrous organic alcohol solvent to obtain a calcium chloride solution, and then adding ceramsite particles coated with a polyvinyl alcohol coating; adding the triethylamine containing a disintegrant dropwise to the calcium chloride solution while stirring and continuously introducing carbon dioxide gas containing saturated water vapor; after the titration is completed, removing the ceramsite particles and drying them to obtain ceramsite particles coated with a disintegrant and a calcium carbonate coating (shell); S5. Dissolving anhydrous calcium chloride in an anhydrous organic alcohol solvent to obtain a calcium chloride solution, then adding ceramsite particles coated with a disintegrant and a calcium carbonate coating, and dropping triethylamine into the calcium chloride solution while stirring and continuously passing carbon dioxide gas containing saturated water vapor. After the titration is completed, removing the ceramsite particles and drying them to obtain ceramsite particles coated with a calcium carbonate coating (waterproof protective shell); As a specific embodiment of the present invention, the anhydrous organic alcohol solvent is anhydrous ethanol or anhydrous methanol.

[0012] In the preparation method provided by the present invention, there are no special requirements for the integrity of the coating in steps S1 to S4, but step S5 must ensure that the coating is complete so as to form a complete waterproof protective shell. Otherwise, the disintegrant will swell in contact with water during the migration of the bridging particles, breaking the shell in advance, which will cause the bridging particles to bond in advance and affect their smooth entry into the cracks of the target formation. In step S3, a polyvinyl alcohol film is provided, which has high viscosity and is convenient for the later bonding of the disintegrant and calcium carbonate precipitation to form a shell. Moreover, the polyvinyl alcohol film can be quickly dissolved in hot water and will not affect the later seepage of the thermosetting resin. Steps S4 and S5 involve the generation of calcium carbonate under trace water conditions. Triethylamine is alkaline and combines with hydrogen ions and chloride ions to generate triethylamine hydrochloride, thereby promoting the generation of calcium carbonate.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The sand flushing temporary plugging agent of the present invention has a strong pressure-bearing capacity. Specifically, in the present invention, the outer shell and the waterproof protective shell are both brittle calcium carbonate shells, which are combined into one and are easily broken when subjected to contact force between particles. A disintegrant is added to the outer shell, which can quickly absorb water and swell when exposed to water, so that the outer shell and the waterproof protective shell are broken into fragments together, increasing the seepage channel of the temperature-sensitive adhesive material, so that the connection points of the integrated structure after solidification are more numerous and denser, and the overall pressure-bearing capacity is stronger; the waterproof protective shell is used to protect the outer shell to prevent the outer shell from absorbing water before reaching the target position. Paraffin is located between the outer shell and the inner shell, and it melts into liquid under formation conditions. On the one hand, this makes the integrated structure formed by the outer shell and the waterproof protective shell more deformed inward when subjected to external pressure, and is more likely to break. On the other hand, paraffin is liquid at formation temperature and has a density difference with water, so it is easy to seep out from the bridging particles, thereby forming a water supply channel between the outer shell and the inner shell, facilitating contact between water and the disintegrant, and providing sufficient water source for the expansion of the disintegrant. DETAILED DESCRIPTION

[0014] The specific implementation methods of the present invention will be clearly and completely described below with reference to examples. Obviously, the examples described are only part of the embodiments of the present invention, rather than all the embodiments.

[0015] In the following examples, the particle size is expressed as "X1-X2 mesh" to indicate that the particles can pass through a sieve of X1 mesh but cannot pass through a sieve of X2 mesh. For example, "16-20 mesh" indicates that the particles can pass through a sieve of 16 mesh but cannot pass through a sieve of 20 mesh.

[0016] In the following examples, silane-modified ceramsite was prepared by the following method: 15 mL of KH-540 (γ-aminopropyltrimethoxysilane) was added to 500 mL of deionized water to obtain a silane coupling agent solution, and then 200 g of ceramsite (16-20 mesh) was added. The mixture was stirred in a sealed water bath at 60°C for 5 h, and then dried at 80°C for 2 hours to obtain silane-modified ceramsite.

[0017] Example 1

[0018] S1. 10 g of epoxy resin (E51) and 2 g of a composite curing agent (curing agent 593 and curing agent dicyandiamide mixed in a mass ratio of 7:3) were added to 50 mL of anhydrous ethanol under stirring, and nitrogen was introduced for deoxygenation for 30 min. Then, 50 g of silane-modified ceramsite was added, and the curing reaction was carried out at room temperature under continuous stirring for 24 h. The temperature was then raised to 70° C. and the curing was continued until the anhydrous ethanol solvent was completely evaporated. The product was dispersed into granules and placed in an oven at 70° C. and dried for 6 h to obtain ceramsite particles coated with epoxy resin. S2, heating 100g of paraffin to 70°C to completely melt it, adding the ceramsite particles prepared in step S1 to the paraffin liquid under stirring, then taking it out to room temperature and letting it stand until the outer wall cools and solidifies, and dispersing the product into particles to obtain ceramsite particles covered with paraffin coating; S3, adding the ceramsite particles prepared in step S2 to a polyvinyl alcohol aqueous solution (polyvinyl alcohol content of 15%) at 90° C. under stirring and letting it stand for 5 minutes, then taking out the ceramsite particles and adding them to dimethyl silicone oil to slowly solidify for 2 hours, then transferring them to anhydrous ethanol and rapidly solidifying for 20 minutes, and finally air-drying them to obtain ceramsite particles covered with a polyvinyl alcohol coating; S4. Add 1.5 g of sodium carboxymethyl starch (powder) to 100 mL of triethylamine and ultrasonically disperse for 10 min to obtain a triethylamine solution containing sodium carboxymethyl starch; dissolve anhydrous calcium chloride in anhydrous ethanol to prepare a saturated calcium chloride solution, take 500 mL of the saturated calcium chloride solution, add the ceramsite particles prepared in step S3, and add the triethylamine solution containing sodium carboxymethyl starch dropwise while stirring and continuously passing carbon dioxide gas containing saturated water vapor (gas flow rate 20 mL / min). After the titration is completed, take out the ceramsite particles and dry them at 60° C. for 1 h to obtain ceramsite particles coated with a disintegrant and a calcium carbonate coating; S5. Dissolve anhydrous calcium chloride in anhydrous ethanol to prepare a saturated calcium chloride solution, take 500 mL of the saturated calcium chloride solution, add the ceramsite particles prepared in step S4, and add 50 mL of triethylamine dropwise while continuously passing carbon dioxide gas containing saturated water vapor (gas flow rate 20 mL / min). Then, take out the ceramsite particles and dry them at 60°C for 1 hour to obtain ceramsite particles covered with a calcium carbonate coating, i.e., bridging particles.

[0019] S6. Use calcium carbonate particles (40-60 mesh) as the filling material, mix the bridging particles and the filling material in a mass ratio of 7:3 to prepare a temporary plugging agent; mix the temporary plugging agent and the plugging base slurry in a mass ratio of 1:10 to prepare a plugging material.

[0020] The composition of the plugging slurry base is: water + 4wt% bentonite + 0.2wt% sodium carbonate + 0.1wt% sodium hydroxide + 0.3wt% sodium carboxymethyl cellulose + 0.4wt% xanthan gum. The above addition amounts are based on the mass of water.

[0021] Example 2

[0022] The difference from Example 1 is that in step S1, the amount of epoxy resin added is 15 g, and the amount of composite curing agent added is 3 g, that is, the thickness of the epoxy resin coating is increased.

[0023] Example 3

[0024] The difference from Example 1 is that the amount of triethylamine added in step S5 is 30 mL, thereby reducing the thickness of the waterproof protective shell.

[0025] Comparative Example 1 The difference from Example 1 is that in step S4, no sodium carboxymethyl starch (powder) is added to the triethylamine solution, and the ceramsite particles obtained are only coated with a calcium carbonate coating.

[0026] Test Example 1 The plugging performance of each plugging material was tested, including the following steps: using a plugging tester containing a wedge-shaped crack model (the crack inlet width of the crack model is 4 mm and the outlet width is 2 mm), stirring the plugging material evenly and adding it to the autoclave upstream of the crack model, and closing the outlet valve of the crack model; starting the displacement pump to increase the pressure in the autoclave to 1 MPa, then raising the temperature of the autoclave and the crack model to 180°C to liquefy the paraffin in the bridging particles and allow the epoxy resin to continue to solidify; turning on the cooling water downstream of the crack model to cool and measure the amount of liquid loss, The outlet valve of the fracture model was opened to displace the plugging material within the autoclave and seal the fracture. Displacement was stopped when the pressure within the autoclave reached 2 MPa. The pressure within the autoclave was maintained at 2 MPa to provide strong contact between the bridging particles, breaking up the outer shell and waterproof protective shell of the bridging particles. The temperature of the fracture model and the autoclave was maintained at 180°C to ensure that the epoxy resin continued to cure and form a monolithic plugging layer. After 2 hours, displacement was continued at a rate of 1 mL / min to gradually increase the pressure within the autoclave. A sudden and sharp drop in the pressure within the autoclave was considered to indicate a breach of the plugging layer, and the experiment was terminated. The peak pressure during the pressure increase process was considered the pressure-bearing capacity of the plugging material. The fluid loss from the initial moment to the end of the 2-hour constant temperature and pressure period was considered the initial loss, and the fluid loss from the initial moment to the peak pressure was considered the cumulative loss. The test results for each plugging material are shown in Table 1.

[0027] Table 1 Plugging performance of various plugging materials

[0028] As can be seen from Table 1, the pressure-bearing capacity of the plugging materials corresponding to Examples 1 to 3 is significantly higher than that of the plugging material corresponding to Comparative Example 1. This is because the former contains a disintegrant (sodium carboxymethyl starch), which absorbs water and expands, causing the calcium carbonate waterproof protective shell and the outer shell to break more fully, increasing the seepage channel of the temperature-sensitive adhesive material (epoxy resin), thereby forming more connection points between the particles, so that the final integrated structure has more connection points, higher density, and stronger pressure-bearing capacity; the pressure-bearing capacity of the plugging material corresponding to Example 3 is significantly greater than that of the plugging materials corresponding to Examples 1 and 2, which indicates that the waterproof protective shell is easier to break as the thickness is reduced; the initial loss of the plugging materials corresponding to Examples 1 to 3 is also significantly lower than that of the plugging material corresponding to Comparative Example 1. This is because the former breaks under the action of the disintegrant to form more and smaller calcium carbonate particles, which can further fill the pores of the sealing layer and reduce the loss.

[0029] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art will appreciate that these embodiments are intended to illustrate the present invention only and are not to be construed as limiting the scope of the present invention. Further improvements may be made without departing from the principles of the present invention, and such improvements are intended to fall within the scope of protection of the present invention.

Claims

1. A sand flushing temporary plugging agent, comprising bridging particles and filling materials, characterized in that: The bridging particles are of a core-shell structure and comprise, from the inside to the outside: a core formed of a compression-resistant material; An inner shell formed of a thermosetting resin and a curing agent, wherein the material in the inner shell can continue to cure and bond into one piece under the temperature conditions of the target formation; an intermediate layer formed of paraffin wax, the melting point of the paraffin wax being lower than the temperature of the target formation; a shell formed of calcium carbonate and a disintegrant; Waterproof protective shell formed from calcium carbonate.

2. A temporary plugging agent for sand flushing according to claim 1, characterized in that: The curing agent includes two curing agents with different triggering temperatures, namely a low-temperature curing agent and a high-temperature latent curing agent, wherein the triggering temperature of the low-temperature curing agent is lower than the triggering temperature of the high-temperature latent curing agent, and the triggering temperature of the high-temperature latent curing agent is lower than the temperature of the target formation.

3. A temporary plugging agent for sand flushing according to claim 1, characterized in that: The disintegrant is sodium carboxymethyl starch granules, low-substituted hydroxypropyl cellulose granules or cross-linked polyvinyl pyrrolidone granules.

4. A temporary plugging agent for sand flushing according to claim 3, characterized in that: The mass content of the disintegrant in the shell is 1% to 6%.

5. A temporary plugging agent for sand flushing according to claim 1, characterized in that: The thermosetting resin is epoxy resin, phenolic resin, bismaleimide resin or cyanate resin.

6. A method for preparing a sand flushing temporary plugging agent, for preparing the sand flushing temporary plugging agent according to claim 1, characterized in that: The steps include: S1, using silane-modified ceramsite as the core and epoxy resin as the thermosetting resin, dispersing the silane-modified ceramsite, epoxy resin and curing agent in a solvent under stirring conditions, heating to preliminarily cure the epoxy resin, then removing the solvent, dispersing and drying the resulting material to obtain ceramsite particles covered with an epoxy resin coating; S2, adding the ceramsite particles covered with the epoxy resin coating to the molten paraffin liquid under stirring, then taking out and cooling to obtain ceramsite particles covered with the paraffin coating; S3, adding the paraffin-coated ceramsite particles to a heated polyvinyl alcohol aqueous solution under stirring, then letting it stand, taking it out to solidify and air-drying it to obtain polyvinyl alcohol-coated ceramsite particles; S4, adding a disintegrant to triethylamine and ultrasonically dispersing it to obtain triethylamine containing a disintegrant; dissolving anhydrous calcium chloride in an anhydrous organic alcohol solvent to obtain a calcium chloride solution, adding the ceramsite particles coated with a polyvinyl alcohol coating, and dropping the triethylamine containing a disintegrant into the calcium chloride solution while stirring and continuously passing carbon dioxide gas containing saturated water vapor. After the titration is completed, the ceramsite particles are taken out and dried to obtain ceramsite particles coated with a disintegrant and a calcium carbonate coating; S5, dissolving anhydrous calcium chloride in an anhydrous organic alcohol solvent to obtain a calcium chloride solution, adding the ceramsite particles covered with a disintegrant and a calcium carbonate coating, and dripping triethylamine into the calcium chloride solution under the condition of stirring and continuously passing carbon dioxide gas containing saturated water vapor. After the titration is completed, the ceramsite particles are taken out and dried to obtain ceramsite particles covered with a calcium carbonate coating.

7. The method for preparing a sand flushing temporary plugging agent according to claim 6, characterized in that: The anhydrous organic alcohol solvent is anhydrous ethanol or anhydrous methanol.

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